1. Field of the Invention
The present invention relates to a dynamoelectric stator core such as for an automotive alternator, etc., and to a method for the manufacture thereof, and particularly relates to a stator core that is prepared by forming slots in core segments having a predetermined length, laminating a large number of the core segments to form a rectangular parallelepiped lamination, and bending the lamination into a cylindrical shape, and to a method for the manufacture thereof.
2. Description of the Related Art
Conventional dynamoelectric stator cores have been prepared by punching strip-shaped magnetic steel plates having a predetermined length so as to have a core root portion and a plurality of tooth portions, preparing a rectangular parallelepiped laminated core by laminating a predetermined number of those plates, then bending the laminated core into a cylindrical shape by winding it onto a cylindrical mandrel member, and finally integrating the laminated core that has been bent into a cylindrical shape by abutting and welding two end surfaces thereof (see Patent Literature 1, for example). This conventional technique has problems such as the abutted surfaces not aligning when the laminated core is bent into a cylindrical shape since the amount of bending at two end portions of the laminated core is less than in other portions, and this has been relieved by bending only the two end portions of the laminated core so as to have a predetermined curvature, and then bending the laminated core as a whole into a cylindrical shape.
Other conventional dynamoelectric stator cores have been prepared by preparing two rectangular parallelepiped laminated core sections by obtaining magnetic steel plates by punching and laminating the plates to a thickness that is half a predetermined thickness, preparing a rectangular parallelepiped laminated core that has the predetermined thickness by laminating the two laminated core sections such that punching directions of the magnetic steel plates are oriented toward each other, and bending that laminated core into a cylindrical shape (see Patent Literature 2, for example). In this conventional technique, the occurrence of damage to an insulating coating of a stator winding due to burrs that are generated during punching has been relieved by laminating the two laminated core sections such that the punching directions of the magnetic steel plate are oriented toward each other.
Since flexing of rollers is unavoidable in the process of rolling rolled steel plates, there are often plate thickness deviations in the width direction of rolled steel plates. If large numbers of annular circular core plates obtained by punching rolled steel plates in which these plate thickness deviations are present are laminated, the thickness of the resulting cylindrical stator core in the direction of lamination has biases relative to a circumferential direction, and biases of magnetic properties in the circumferential direction adversely affect the characteristics of the dynamoelectric machine.
In view of these conditions, laminated thickness has been made uniform relative to a circumferential direction of a stator core by changing the angle of circular core plates that were punched from rolled steel plates as each plate was laminated (see Patent Literature 3, for example). Laminated thickness has also been made uniform relative to a circumferential direction of a stator core by preparing a plurality of circular core plate groups by laminating a predetermined number of circular core plates that were punched from rolled steel plates, and then changing the angle of and laminating a plurality of the circular core plate groups (see Patent Literature 4, for example). Laminated thickness has also been made uniform relative to a circumferential direction of the stator core by preparing two half cores by laminating circular core plates that were punched from rolled steel plates to a thickness that was half a predetermined thickness, and then inverting one half core and laminating it onto the other half core (see Patent Literature 5, for example).
[Patent Literature 1]
Japanese Patent Laid-Open No. 2001-298885 (Gazette)
[Patent Literature 2]
Japanese Patent Laid-Open No. 2003-37951 (Gazette)
[Patent Literature 3]
Japanese Patent Laid-Open No. HEI 05-168178 (Gazette)
[Patent Literature 4]
Japanese Patent Laid-Open No. HEI 09-117111 (Gazette)
[Patent Literature 5]
Japanese Patent Laid-Open No. SHO 58-159640 (Gazette)
In the techniques described in Patent Literature 1 and 2, no consideration at all has been given to problems due to plate thickness deviations in the rolled steel plates. Thus, in techniques in which a stator core is prepared by bending a rectangular parallelepiped laminated core into a cylindrical shape, as described in Patent Literature 1 and 2, because two ends of the strip-shaped magnetic steel plates, i.e., remotest portions of the magnetic steel plates are abutted to each other, plate thickness deviations in the width direction of the rolled steel plates are superposed and give rise to laminated thickness differences that cannot be ignored. Large differences in level thereby arise at the abutted portion of the stator core. In dynamoelectric machines that have stator cores of this kind installed, exchanges of magnetic flux between the teeth of the stator core and the magnetic poles of the rotor core are disturbed by the teeth that have differences in level, thereby reducing magnetic circuit characteristics and also giving rise to electromagnetic noise that results from distortion of the magnetic flux, thereby reducing quality.
The techniques described in Patent Literature 3 through 5 prepare stator cores by laminating circular core plates that are punched from rolled steel plates and are difficult to apply to techniques in which a stator core is prepared by bending a rectangular parallelepiped laminated core into a cylindrical shape for the reasons described below.
First, in the stator cores described in Patent Literature 1 and 2, plate thickness deviations in the rolled steel plates give rise to differences in level at the abutted portion of the laminated core that has been bent into a cylindrical shape. In the stator cores described in Patent Literature 3 through 5, on the other hand, plate thickness deviations in the rolled steel plates give rise to biases in plate thickness in a circumferential direction. Thus, since the methods for manufacturing a stator core differ, the problems arising as a result of plate thickness deviations in the rolled steel plates are also completely different.
Second, because longitudinal direction of the magnetic steel plates is limited to being in a width direction of the rolled steel plates or a feed direction of the rolled steel plates if consideration is given to yield when long magnetic steel plates are punched from rolled steel plates, the degree of freedom is extremely small compared to when circular core plates are punched. Consequently, it is not very realistic to change the longitudinal direction (position) of the magnetic steel plates while punching magnetic steel plates from rolled steel plates to allow for plate thickness deviations in the rolled steel plates. In addition, approximately three times as much workspace is required if two laminations of long magnetic steel plates are inverted and laminated than if half cores that are made by laminating circular core plates are inverted, and increases in man-hours and cost cannot be prevented, making such techniques unrealistic.